1. Field of the Invention
The present invention generally relates to vascular stents.
2. State of the Art
A stent, generally speaking, is a device that can be placed within the lumen, or interior space, of a tubular structure for supporting and assuring patency of a contracted, but otherwise intact, lumen. (Patency, the state of being freely open, is particularly important in the field of angioplasty, which is concerned with the reconstruction of blood vessels.) Stents are used, for example, for holding blood vessels open or for back tacking intimal flaps inside vessels after angioplasty. More generally, however, stents can be used inside the lumina of any physiological conduit including arteries, veins, vessels, the biliary tree, the urinary tract, the alimentary tract, the tracheobronchial tree, the genitourinary system, and the cerebral aqueduct. Furthermore, stents can be used inside lumina of animals other than humans.
In the field of angioplasty, the most common angioplasty surgical procedure is percutaneous transluminal coronary angioplasty, or "PTCA", which is employed for enlarging narrowed arteries near the heart. In a PTCA procedure, a balloon-tip catheter is maneuvered into position in a narrowed artery where the balloon is expanded in order to dilate this area of narrowing. After the arterial lumen is dilated, the balloon at the catheter tip is deflated and the catheter is removed from the enlarged artery. A vascular stent can be used to dilate an artery after a suboptimal PTCA dilation.
In practice, the above-described conventional PTCA procedure has several shortcomings. One drawback is that approximately one-third of all PTCA patients suffer from restenosis, a chronic regrowth of obstructive tissue that narrows the lumen. Typically, restenosis occurs within six months following an angioplasty procedure. Since a majority of these restenosis patients also display symptoms of deteriorating cardiac status, they frequently must undergo additional PTCA procedures or more risky coronary artery bypass graft surgery. Unfortunately, those patients who undergo repeated PTCA procedures tend to restenose at an even higher rate than first-time PTCA patients.
A second, and sometimes fatal, complication of coronary angioplasty is the abrupt re-closure of a previously dilated section of a vessel. There are many different factors that are thought to contribute to abrupt re-closure after PTCA including obstructive flaps of disrupted wall tissue, vessel wall spasms with luminal contraction, and thrombus formation at the site of dilation. Vascular stents can be used like a scaffold to mechanically bridge areas of narrowing (flaps or thrombus) and oppose spasms, and therefore, maintain artery patency.
Many of the factors responsible for abrupt closure (post balloon inflation) may also influence the development of restenosis, and therefore, long term patency. In this regard, vascular stents, by virtue of their ability to limit elastic recoil of the vessel wall and to eliminate the negative physical consequences of PTCA (including obstructing intimal flaps and dissection) may be useful in limiting restenosis.
Therefore, there are two potential benefits of vascular stents in the treatment of vascular disease: 1) prevention of abrupt arterial closure, and 2) prevention of restenosis.